Mercury MerCruiser MCM 454 Mag MPI Service Manual page 566

SERVICE MANUAL NUMBER 23
A scan tool can be used to help detect intermittent conditions. The scan tool has several
features that can be used to locate an intermittent condition. The following features can be
used in finding an intermittent fault:
The "Record" feature (if equipped) can be triggered to capture and store engine parameters
within the scan tool when the malfunction occurs. This stored information then can be
reviewed by the service technician to see what caused the malfunction.
To check loss of DTC memory, disconnect TP sensor and idle engine until the MIL comes
ON. A trouble code should be stored and kept in memory when ignition is turned OFF. If not
the ECM is faulty. When this test is completed, make sure that you clear the DTC 22 from
memory.
An intermittent MIL with no stored DTC may be caused by the following:
All Ignition Control (IC) module wiring should kept away from the alternator. Check all wires
from the ECM to the ignition control module for poor connections.
Index
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Ignition coil shorted to ground and arcing at ignition wires or plugs.
MIL wire to ECM shorted to ground.
Poor ECM grounds, Go to ECM wiring diagrams.
Check for an electrical system interference caused by a sharp electrical surge. Normally,
the problem will occur when the faulty component is operated.
Check for improper installation of electrical options such as lights, ship to shore radios,
sonar, etc.
Check that knock sensor wires are routed away from spark plug wires, ignition system
components and charging system components.
Check for secondary ignition components shorted to ground, or an open ignition coil
ground (coil mounting brackets).
Check for components internally shorted to ground such as starters, alternators or
relays.
FUEL INJECTION SYSTEM TROUBLESHOOTING
Page 5D-7